To fabricate microelectronic semiconductor devices such as an integrated circuit (IC), many different layers of metal and insulation are selectively deposited on a silicon wafer. The insulation layers may be, for example, silicon dioxide, silicon oxynitride, fluorinated silicate glass (FSG), carbon doped, silicon dioxide or organosilicad glass (OSG) and the like. These insulation layers are deposited between the metal layers, i.e., intermetal dielectric (IMD) layers, and may act as electrical insulation therebetween or serve other known functions. These layers are typically deposited by any well known method such as, for example, plasma enhanced chemical vapor deposition (PECVD), chemical vapor deposition (CVD) or other processes.
The metal layers are interconnected by metallization through vias etched in the intervening insulation layers. To accomplish this, the stacked layers of metal and insulation undergo photolithographic processing to provide a pattern consistent with a predetermined IC design. By way of example, the top layer may be covered with a photo resist layer of photo-reactive polymeric material for patterning via a mask. A photolithographic process using either visible or ultraviolet light is then directed through the mask onto the photo resist layer to expose it in the mask pattern. An antireflective coating (ARC) layer such as PECVD SiON or spin on coating materials may be provided at the top portion of the wafer substrate to minimize reflection of light back to the photo resist layer for more uniform processing. The spin on ARCs may include AR-1 4™ (manufactured by Shipley Company, LLC of Marlborough, Mass.) or sacrificial light absorbing material (hereinafter referred generally as SLAM).
To form vias, for example, etching may be used to connect the metal layers deposited above and below the insulation or dielectric layers. The etching may be performed by anisotropic or isotropic etching as well as wet or dry etching, i.e., RIE (reactive ion etching), depending on the physical and chemical characteristics of the materials. To maximize the integration of the device components in very large scale integration (VLSI), it is necessary to increase the density of the components. This requires very strict tolerances in the etching and photolithographic processes.
However, it is known that resist poisoning can occur during the photolithographic processes. One example of resist poisoning during the lithographic process is caused by amine-induced poisoning of chemically amplified resists created during the patterning step. This may be caused when low k dielectrics are used for the IMD and interlevel dielectric (ILD). In a more general example, during the photolithographic process, contaminants that are incompatible with the photo-reactive polymeric material can migrate into the photo resist layer from the deposited film on the wafer, itself. These contaminants then poison the photo resist layer, which may result in a non-uniformity of the reaction by extraneous chemical interaction with the polymeric material. The resist poisoning also may result in poor resist sidewall profiles, resist scumming and large CD variations. This leads to the formation of a photo resist footing or pinching, depending on whether a positive negative or photo resist, respectively, is used during the process. This may also lead to an imperfect transfer of the photo resist pattern to the underlying layer or layers thus limiting the minimum spatial resolution of the IC.
One known method to solving this problem is to run a totally free nitrogen or nitrogen containing molecule free process. Examples of nitrogen containing molecules include N2, NH3, NO, NO2, etc. However, all released FSG films are known to require either N2O (silane films) or N2 (TEOS) films. In addition, silicon nitride or silicon carbon nitride is commonly employed as a copper cap under the IMD due to its superior electromigration performance as compared to silicon carbide. Finally, even if totally nitrogen free films are used, nitrogen from the ambient air, ARC/photoresist or nitrogen impurities contained in the deposition or etch gases can result in the presence of amines.